Well casing joint



March 15, 1938.` H. G. TEXTER WELL CASING JOINT Filed Feb. 2e, 1935,

INVENTOR.

BY /W/IALCM# 75;. 'ATTORNEYA l l l l I I I I I I I MHT@ I.

atented ar. l5, i3

WELL oasrNG .rorN'r Howard G. Texter, rIullsa, kla., assigner, by mesne assignments, to The National Supply Company, Pittsburgh, Pa., a corporation of Pennsylvania v Application February 26, 1935, Serial No. 8,278

4 claims. (ci. 2st-.146i` The invention relates to oil Well casing formed of a plurality of lengths of tubes connected endto-end by threaded joints. f

In drilling an oil Well'the practice is, as the 5 drilling progresses, to line the hole with casing :formed of seamless or other types of tubing, depending, among other things, upon the location of thecasing and the size of the hole. For example, a hole of relatively large diameter ma?)7 be drilled to a depth of 500 feet after which a string of casing of a suitable relatively large diameter is placed in the hole. Thereafter the drilling of a hole of a smaller diameter proceeds f through and below the rst casing until it is necessary or desirable to insert another casing of smaller diameter than that at the top of the hole, which procedure is continued until the well is completely drilled; each string of casing extending to the top of the well.

In setting a string of casing, whether it extends from the topto the bottom or to an intermediate level in a well, successive lengths of tubes are connected to each other at the top of the well and the casing progressively lowered, the weight of the casing being sustained by the bodies of the individual tubes and by their connecting threaded joints. This makes it necessary to provide joints of substantial strength and high efficiency. Joint eliiciency, as understood by those skilled in the art, and as hereinafter used, is the percentage ratio of the ultimate strength of the joint divided by the ultimate strength of the connected tubing. Joint strength, on the other hand, is measured by the actual tensional pull required to produce failure of the joint. Joint strength includes rst the yield point of the joint, and second the ultimate strength of the joint at break.

It is occasionally necessary to pull a string of casing from a well by engaging the top of the casing and progressively raising it and unscrewing the joints to disassemble the` casing as it is pulled. For this purpose also, it is necessary to provide joints having substantial' strength because some of the joints must sustain the weight of casing several thousand feet in length and as well as overcoming the frictional resistance between the casing and the wall of the drilled hole. Strings of casing are frequently so pulled from a Well when a dry hole is drilled, when a well has run its life and the casing has not been destroyed or impaired by corrosion or otherwise,

when in the running of a string of casing it sticks in the well making it necessary to withdraw it and drill out the obstruction, and also when a line of casing is accidentally dropped into a well which makes it necessary to sh it out.

In providing joints for well casing the prevailing practice has been to endeavor to make them as strong as possible, and'in fact as strong as the tensile strength of the tubes forming the casing, which would be 100% efficiency. However, this end has not been attained in joints made according to the standard Well-recognized specications of the American Petroleum Institute, particularly in joints for larger sizes of casing, say l0 inches and upwards in diameter. If a string of casing is provided with joints which are as strong as the body of the tubing of which the casing is formed, in the pulling of the string it may break in the body of one of its tube lengths or at a joint, and in either event a long string of casing may stretch several hundred feet over-all, with the bodies of the tubes, or

the joints, or some of them, stretching beyond g their elastic limit which renders them unsuitable for future use. If a string of casing breaks from axial tension in the body of the tube the metal thereof necks down to such an lextent that it is diiiicult or impossible shing tools. Thus net only is the casing lost, but likewise the Well may have to be abandoned. The object of my invention is to provide a string of oil well casing having joints of high strength but nevertheless of such strength with relation to that of the tubes of which the casing is formed that a break in the string will occur at a joint. r In the practice of my invention I provide a string of oil well casing formed of a plurality of tubes connected end-to-end by threaded joints, each of which is so formed that its ultimate strength under tension longitudinally of the casing is not less than the yield point ofthe tubes connected by the joint, and each of which has an ultimate strength materially less than that of the ultimate strength of its connected tubes. The words joint ultimate strength materially less than the ultimate strength of the tubes are meant to dene that llilmit at which the stress has exceeded thcyield point of the tube but not caused objectionable or material permanent elongation or plastic flow. By thus establishing the joint strength with relation to that of the tube lengths, any break that occurs in the string will be at a joint rather than in the body of a tube length, but the joints are nevertheless of such strength that none of them breaks before liability of lmpairing their connected tube lengths by stretching the tubes beyond their elastic limit.

to engage the tubing by g l include an inner string 2 extending from the top The invention is illustrated in the accompanyof tubes of diierent wall thickness as a matter ing drawing of which Fig. 1 is a diagrammatic, cross-sectional view of an oil-well casing program, and Fig. 2 a longitudinal central sectional view'of one form of joint that may be used in the practice of the invention.

Having reference to Fig. 1, a Well I is shown as being provided with a casing program consisting of a plurality of strings of casing, which may to the bottom of the Well, an intermediate string 3 of larger diameter extending from the top to an intermediate level, and a string 4 of still larger diameter extending from the top to an intermediate level above that at the bottom of string 3. Each of the casing strings 2, 3 and 4 is formed of lengths of tubing connected to each other by threaded joints 5,'6 and 'l respectively.V

The joints may be of any particular type so long as their strength and eiciency is made within the limits heretofore described. The joint, disclosed in Patent No. 1,927,656 to Eaton and Burnish, and an improved form thereof disclosed in patent application vSerial No. 7,212, led February 19, 1935, by George M. Eaton, is capable of being made with high strength and eillciency. I have found that by establishing the proper upsetting, machining and threading operations that vthe George M. Eaton joint can be made to fulfill the objects of my invention.

A joint of the Eaton type has been illustrated in Fig. 2 of the drawing and includes threaded male and female portions Ill and Il formed integrally With the respective tube lengths. In making the joint, the pipe ends are upset to provide the necessary thickness for strength and then are machined internally and externally to exact, desired, concentric diameters. Complernentary, sturdy, trapezoidal threads, and also sealing surfaces, if desired, are the'n machined on the male and female members with the taper of the threads being relatively steep and with a relatively small number of threads per inch. The threads are preferably formed with at crests and roots parallel to the axis of the jointlv While the joint strength may vary within the limitation that the ultimate strength of the joint is not less than the yield point of its adjoining tubes, and is materially less than the ultimate strength of such tubes, the efciency of each joint is preferably about 85%. It should be appreciated that the particular strength of each of economy, although that is not the prevailing practice which is to form a string of casing from tubes of uniform wail thickness. In the latter event, all of the joints of the casing are of uniform strength as well as of uniform elciency.

By providing a string of casing With joints of the herein described eiiciency the advantages of my invention are attained, they being that in case the string breaks when it is being pulled from a Well or under other circumstances, it will break at a joint rather than in the body of one of its tube lengths which makes it difficult, and sometimes impossible to sh the remainder of the string from a well. Likewise by making my joint elciency, throughout each string, approximately 85%, rather than a materially higher eciency, I am able to reduce the outer diameters of the joints and increase the inner diameters with the attending advantages of smaller starting well diameter while maintaining the same bottoming well diameter.

According to the provisions of the patent statutes, I have explained the principle'and mode of operation of my invention, and have illustrated what I now consider to represent its best embodiment. However, I desire to have it understood that Within the scope of the appended claims vthe invention may be practiced otherwise than as specifically illustrated and described.

I claim:

1. A string of oil-well casing formed of a plurality of tubes connected end-to-end by threadedl joints, each joint being formed to have an efciency of about 85 per cent.

2. An oil-well casing program comprising a plurality of nested Strings of casing, the joints of said strings being formed to have a uniform efficiency throughout the program and each joint being formed to have an ultimate strength not less than the yield point of the casing joined thereby but being materially less than the ultimate strength of such casing, whereby in case any string breaks the break will occur at a joint prior to material elongation of the string.

3. A string of oil-well casing formed of a plurality of tubes connected end to end by threaded joints, the joints in at least the upper portion of the casing being formed to have an efliclency of about 85 per cent.

4. An oil-well casing program comprising a plurality of nested strings of casing, the joints of at least two of said strings being formed to Vhave a substantially uniform eiliciency throughout the program and each joint being formed to have an ultimate strength not less than the yield A HOWARD G. 

